Crystal control circuit



Dec. 15, 1936, '11P. KINN CRYSTAL CONTROL CIRCUIT Filed June 9, 1954 l INVENTOR WITNESSES:

' ATTORNY Patented Dec. 15, 1936 UNITED STATES PATENT OFFICE CRYSTAL CONTROL CIRCUIT of Pennsylvania Application June 9, 1934, Serial No. 729,814

4 Claims.

This invention relates to crystal-controlled oscillation generators and particularly to that type of such generators in which the interelectrode capacity is supplemented by a condenser con- 5 nected across the plate and grid externally of the tube.

It is an object of this invention to obtain a greater effectiveness of feed back and thereby a greater certainty in starting oscillations with- 10 out increasing the danger of breaking the crystal.

It is a further object of this invention to afford means for protecting the crystal from the effects of too great a current through the crystal holder.

15 It is a further object of this invention to provide means for adjusting the phase of the potential impressed on the grid of the vacuum tube with respect to that on the plate. By making this phase difference between plate and grid potential exactly 180", the maximum effectiveness of the potential impressed across the crystal is obtained. The circuit is placed at the most efficient oscillating point thereby requiring very small feed-back to produce oscillation.

It is a further object of this invention to increase the impedance presented to current through the capacity of the crystal holder.

Other objects of this invention and details of the construction will be apparent from the following description and the accompanying drawing, in which Figure 1 is a diagram of one embodiment of my invention, and

Fig. 2 is a similar diagram of another em- 35 bodiment.

In both systems, the tube I is equipped with a filament 2 which is supplied from any suitable source of power, represented by the transformer 3. The plate battery 4 is connected through the tank circuit 5 to the plate of the tube I and to the filament. The screen grid 6 is connected to an intermediate point of the battery 4 and the portion of the battery between this point and the filament is shunted by a by-pass con- 45 denser 1. A by-pass condenser 8, shunting the whole battery is connected between the filament and the tank circuit. The control grid II is connected to the filament through a circuit including the crystal 12 which is mounted in any 50 suitable holder. An adjustable condenser I3 is connected between the control grid II and the plate of the tube.

The connections between the control grid II and the crystal l2 include an inductor 14. The

55 inductance of this coil is preferably too small for it to act as a radio-frequency choke. A resistor I5 is connected in shunt to the crystal. In Fig. l, the connection of the resistor is from the junction of the coil l4 and crystal l2. The inductor I4 is thus omitted from the shunted 5 portion of the grid circuit. In Fig. 2, the con nection to the resistor i5 is between the control grid II and the inductor l4, whereby the inductor is included in the shunted portion of the grid circuit.

An ammeter I! and an adjustable condenser IS in series with the crystal are included in the shunted apparatus in each form of the invention. The condenser 18 may be on the other side of the crystal from its illustrated position and, in the form illustrated in Fig. 2, it may even be on the opposite side of the inductor It.

In the operation of the device, as illustrated in Fig. 1, the vacuum tube generates oscillations in the familiar way and this action need not be 20 described. The effect of the inductance I4 is to present a substantial impedance to the frequency of the oscillations. The potential delivered to the crystal i2 is smaller because of this impedance. If the inductance of the coil 14 is so chosen that within the tuning range of the condenser l3 a series-resonant connection is established between the plate and the crystal for the frequency corresponding to the crystal, the voltage delivered to the crystal will be exactly 180 out of phase with the plate potential. The voltage delivered to the crystal is then of a phase which is most effective in causing the oscillation generator to start. If desired, the condenser 13 may be set at this value when starting the generator and adjusted somewhat away from this value after oscillations have built up.

The condenser l8 being in series with the capacity of the crystal holder I2 causes the combination of the two capacitors to present a large impedance to oscillations of the frequency of the crystal. The resistor l5 in shunt to this impedance will, therefore, convey most of the current which otherwise would be carried by the capacity of the crystal holder I2.

It is the current flowing through the crystal holder, by virtue of its capacity, which is most likely to cause brush discharges or other actions tending to disrupt the crystal. The minimizing of such current, which results from diminishing the potential by the inductor l4 and increasing the impedance shunted by the resistor 15, protects the crystal effectively even when the inductor I4 is of a magnitude which results in a series-resonant connection between the plate and the crystal.

Various modifications of this invention will be evident to those skilled in the art. The specific illustration and description of two forms of the invention only is not to be regarded as a limitation. No limitations are intended unless required by the prior art or expressed in the claims.

I claim as my invention:

1. In a crystal-controlled oscillator, an electron discharge device comprising cathode, anode and grid elements, a piezo-electric crystal and electrodes therefor, said electrodes being connected in a circuit between the cathode and another of said elements, an inductance in series with said crystal in said circuit and a capacity connected between the third of said elements and said other element, said inductance and said capacity comprising a circuit tuned substantially to the frequency of the crystal,

2. In a crystal-controlled oscillator, an electron discharge device comprising a cathode, anode and grid elements, a piezo-electric crystal and electrodes therefor, said electrodes being connected in a circuit between said grid and cathode elements, an inductance in series with said crystal in said circuit and a capacity connected between said anodeand said grid, said inductance and said capacity comprising a circuit tuned to the frequency of the crystal.

3. In a frequency controlled oscillator, an

electron discharge device comprising cathode, anode and grid elements, a vibratile frequency determining element and electrodes therefor, said electrodes being in capacitive relationship to each other and connected in circuit between two of said elements, means in said circuit to enhance the impedance offered to the flow of current through said vibratile element by the capacity existing between its electrodes, an impedance lower in value than that of the combined electrode capacity and the impedance of said last means, said impedance comprising a path for the flow of current around said vibratile element and its electrodes, and a series tuned circuit, including a portion of said circuit between one of the electrodes and one of the elements, tuned to the frequency of said crystal and connected between another of said elements and said one electrode of said crystal.

4. In a crystal-controlled oscillator, an electron discharge device comprising a cathode, anode and grid elements, a piezo-electric crystal and electrodes therefor, said electrodes being connected in a circuit between said grid and cathode elements, an inductance in series with said crystal in said circuit and a variable capacity connected between said anode and said grid, said inductance and said capacity comprising a circuit tuned substantially to the frequency of the crystal.

THEO. P. KINN. 

